The present invention relates generally to molding processes and articles molded thereby and, more particularly to an improved molding process in which decorative films are formed with the forming of the article to enhance the cosmetic appearance thereof.
Injection molding is used widely to produce numerous articles. These articles range from articles with simple configuration such as plates, light switches and the like to more complex molded shapes, such as wireless telephone housings. These molded articles often need to be decorated to enhance their visual appeal and their saleability. Some such articles may be decorated in the simplest sense of the term, by either adding pigments to the pellets of plastic used in the injection molding process or by using colored pellets to mold the article. Although these two methods are effective for coloring the molded article, they result in solid coloring of the article and are ineffective in forming any complex decorative appearance to the molded article.
Some other processes are known in the injection molding art for decorating molded products. One such process involves the use of stamping or otherwise applying a foil layer to the exterior of the molded product. In this process, the foil is applied to the molded article after the article is molded and from the molding machine. This metal foil is thin and is prone to breakage on sharp corners and complex curves of the molded article. Registration problems are also encountered with this process.
Another process for decorating molded articles involves the use of xe2x80x9cpadxe2x80x9d printing in which colors or designs are applied to the molded article after molding, by way of one or some more printing pads. These pads are formed of foam rubber or other pliable material and have one or more inks deposited on their exterior surfaces, which are subsequently applied to the molded article. Problems exist in that the pad may not contact all the intended surfaces of the article and thus may not accurately apply the ink(s) to all surfaces, especially complex surfaces of the molded article. Similarly, the exterior surface of a molded article may serve to frustrate the use of screen printing the molded article. Hydrographics, the use of floating a decal in water and then applying it to the molded article, has its own limitations in that the decals are prone to tearing and there exist great difficulties in accurately registering the decals in place on a complex molded article.
In-mold decorating is yet another process that has been used to decorate injection molded articles. This process involves introducing a decorative film into the mold cavity. However, the film is delicate and fragile. It also has registration problems with complex molded articles inasmuch as the film inserted into the mold cavity is die cut. The walls and surfaces of the mold cavity are used for registration of the film in the mold cavity, and the mold cavity may not be modified to create any registration means. As such, this process is effectively limited to application to flat surfaces in the mold and on the final molded article, such as label recesses. It also cannot provide any details along the z-axis of the mold cavity or along the sides of the finished molded article.
A still further process involves the use of a decorative xe2x80x9cpreformxe2x80x9d, where an outer, decorative shell is formed complying to the configuration of the final molded article and it is inserted into the mold cavity prior to the injection of liquid plastic or other molding material into the mold cavity. The shape of this preform must conform accurately to the final configuration of the molded article. Where openings are molded into the article during the molding process, registration between the preform and the mold cavity must be critically maintained. Thin wall portions of the preform may result in leakage of the injected melt and problems with the finished article, leading to high rejection rates.
A need therefore exists for an improved molding process for decorating the surfaces of a molded article that complements the usual operational parameters of the molding process and which overcomes the aforementioned disadvantages of the prior art.
The present invention is therefore directed to a molding process in which a decorative film is applied to the exterior surface of a molded article.
Accordingly, it is a general object of the present invention to provide an improved molding process in which a decorative film is formed onto the exterior surface of a molded article during the actual molding thereof.
Another object of the present invention is to provide a hybrid injection molding process in which a decorative film is first prepared and subsequently intimately attached to a molded article by drawing the decorative film into a mold cavity, injecting a liquid melt into the mold cavity so that an intimate attachment results between the molded article and its associated decorative film.
Still another object of the present invention is to provide an improved molding process in which a film sheet is decorated with a preselected decorative pattern is applied in registration with a mold cavity, the film sheet is heated and drawn into the mold cavity by negative air pressure so that the film sheet is in contact with substantially all of the mold cavity interior surfaces, and a liquid melt, typically a liquid plastic, is injected into the mold cavity so that it entirely fills the mold cavity and contacts the film sheet so that when the liquid melt is cooled and the article is ejected from the mold cavity, the film sheet is intimately attached to the molded article.
Yet another object of the present invention is to provide a molding process for forming decorative molded articles that includes the following steps: modifying a mold cavity, preferably the core side, to include registration means for maintaining a decorative film sheet in registration with the mold core cavity; applying the decorative film sheet to the mold core cavity; softening the decorative film sheet; applying negative air pressure to at least a portion of the mold core cavity to drawn the decorative film into the mold core cavity and at least into partial contact with the surfaces of the mold core cavity; bringing an opposing mold detail member into engagement with the mold core to form a final mold cavity; and, injecting a liquid molding compound into the mold-cavity under pressure to form a molded article, the decorative film sheet being bonded to the molded article along substantially all of the exterior surfaces of the molded article.
A still further object of the present invention is to provide a molding machine for performing a hybrid molding process in which a decorative film sheet is drawn into one of two coacting mold blocks in order to contact the interior surface of the one mold block, and a heated molding compound is injected under pressure into the mold cavity so that the decorative film sheet becomes bonded to the molded article, the molding machine having means for holding the film in place over one of the two mold blocks and in registration with the mold cavity of the one-mold block, the machine further having means for drawing the decorative film sheet into the one mold block through the cavity of the one mold block and means for maintaining the film sheet in place during injection of molding material into the mold cavity.
A yet still further object of the present invention is to provide a unique molded article having a body portion and an exterior decorative portion, the two portions of the molded article being intimately attached to each other.
Yet a further object of the present invention is to provide a decorative sheet for insertion into a mold cavity and subsequent attachment thereof to a molded article during the molding of the article, the sheet having a decorative area defined thereon that includes a decorative pattern for attachment to the molded article, the decorative area being printed, painted or otherwise formed, the decorative area having a surface area that is generally no smaller than a corresponding surface area of the mold cavity, the decorative sheet including means for registering the sheet and the decorative area in alignment with the mold cavity, the decorative sheet registration means engaging a complementary registration means formed on one of the mold blocks of the molding machine, preferably the mold cavity or core block, and the decorative sheet further having a flat profile so that it can be easily interposed and held in place between the two molding blocks of the molding machine during the molding process.
Another object of the present invention is to provide an injection molding machine that is adapted for hybrid molding in which a film is inserted into the mold cavity, as part of the injection molding process, the molding machine having at least two opposing mold blocks, one of the two mold blocks including a mold core portion and the other of the two mold blocks including a mold detail portion, the molding machine further including a member that is selectively interposed between the two mold blocks to, in essence, xe2x80x9ccapturexe2x80x9d a film sheet therebetween, the captive member and at least one of the two mold blocks having cooperating means for registering the film sheet with the one mold block, one of the two mold blocks including a porous insert that forms a portion of the mold cavity, the porosity of the insert enabling negative air pressure to be applied thereto so that a portion of the film sheet may be drawn into the mold cavity.
These and other objects of the invention are enabled by the unique steps set out in the methods of the present invention and by the novel structure of certain aspects of the equipment used in methods of the invention.
As exemplified by one embodiment of the invention, a molding machine that has two mold coacting mold blocks, one mold block providing a mold core and the other mold block providing a mold core detail, is modified to accept a decorative film sheet in place over one of the mold blocks, preferably that providing the mold core. The mold core block has means for registering the decorative film sheet in a preselected position between the two mold blocks, such as a plurality of raised pins extending axially outwardly from the outer surface of the mold core block. These registration pins are disposed outside the perimeter of the mold core so that a placement mechanism may be used to apply the film sheet to the mold core block.
The placement mechanism preferably takes the form of a robotic placement arm that is movable in three different spatial axes, such as conventional x-axis, y-axis and z-axis so that proper placement of the decorative film sheet may be assured. The placement mechanism may include a film gripping means such as vacuum-driven cups that selectively contact predetermined portions of the film sheet and can release it on demand. The placement arm may have hollow portions associated therewith that serve to mate with the raised registration pins of the mold core block.
The molding machine also incorporates a retention mechanism that holds the film in place, and captures it in a position on the mold core block and between the mold core and detail blocks. This utilizes a novel retention plate that is held in place over the film sheet and over the mold core block by an electromagnetic system that is capable of selective energization, that when energized, clamps the film sheet in place across the parting line of the mold core block. This retention plate may utilize its electromagnetic attachment aspect to attach itself to either of the two mold blocks of the machine so that it may be initially attached to the mold core block and then attached to the mold core detail block when the two mold blocks are opened. A heat source that is selectively movable in and out of heating contact with the film sheet is also provided and is utilized to soften the film sheet so that is may be more easily drawn into the mold cavity. This heating contact occurs by means of an opening formed in the retention plate.
The mold core block preferably includes a mold core insert disposed therein that is formed from a porous metal insert. A vacuum is drawn on the mold core cavity by way of these pores when negative air pressure is applied to the mold core cavity, thereby negating the need for modifying either the mold core or the mold detail with vacuum passages that may weaken the overall strength of the mold core and its cavity. By using this porous insert, the vacuum is drawn evenly through the mold core cavity and the decorative film is uniformly drawn into the mold core cavity. Once the film is drawn into the mold core cavity, the mold detail is moved into the mold core cavity and a liquid molding material is injected into the resultant cavity. The injected molding material attaches itself to the film sheet that overlies the mold core cavity and assists in moving the film sheet to the outer reaches of the mold core cavity, to the extent that the vacuum drawing step has not accomplished this. The porosity of the entire, or selected porions of the mold core cavity, permits complex geometric shapes to be molded with an outer and sometimes decorative skin integrally attached to the final molded article.
After the decorative film is drawn into the mold cavity, the two mold blocks are brought together to close and seal the mold cavity. An injection nozzle is brought into contact with the mold blocks and, in the preferred embodiment of the invention, is brought in from the mold core side of the mold cavity. Its initial injection of molding material pieces through the film sheet drawn into the mold. Molten molding material then fills the cavity against the film sheet and becomes bonded to it. The injection pressure of the molding material also serves to force any remaining portions of the film sheet into contact with the mold core cavity.
In accordance with a second embodiment of the invention, when the liquid molding material is injected, and typically the injected material will be a heated and liquefied plastic, a homogenous one-piece plastic part is formed with an integral xe2x80x9cskinxe2x80x9d applied to the exterior surface thereof. The film sheet may be applied to either to exterior or to the interior surfaces of the final molded part by simply attaching the decorative film sheet to either the mold core or detail mold block. The film may have any one of a number of different designs disposed thereon and by different means such as screen printing, photolithography for example.
These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description.